13,277 research outputs found
Nonlocal magnon spin transport in yttrium iron garnet with tantalum and platinum spin injection/detection electrodes
We study the magnon spin transport in the magnetic insulator yttrium iron
garnet (YIG) in a nonlocal experiment and compare the magnon spin excitation
and detection for the heavy metal paramagnetic electrodes platinum (Pt|YIG|Pt)
and tantalum (Ta|YIG|Ta). The electrical injection and detection processes rely
on the (inverse) spin Hall effect in the heavy metals and the conversion
between the electron spin and magnon spin at the heavy metal|YIG interface. Pt
and Ta possess opposite signs of the spin Hall angle. Furthermore, their
heterostructures with YIG have different interface properties, i.e. spin mixing
conductances. By varying the distance between injector and detector, the magnon
spin transport is studied. Using a circuit model based on the
diffusion-relaxation transport theory, a similar magnon relaxation length of ~
10 \mu m was extracted from both Pt and Ta devices. By changing the injector
and detector material from Pt to Ta, the influence of interface properties on
the magnon spin transport has been observed. For Ta devices on YIG the spin
mixing conductance is reduced compared with Pt devices, which is quantitatively
consistent when comparing the dependence of the nonlocal signal on the
injector-detector distance with the prediction from the circuit model.Comment: 7 pages, 4 figure
Exciton storage in CdSe/CdS tetrapod semiconductor nanocrystals: Electric field effects on exciton and multiexciton states
CdSe/CdS nanocrystal tetrapods are interesting building blocks for excitonic circuits, where the flow of excitation energy is gated by an external stimulus. The physical morphology of the nanoparticle, along with the electronic structure, which favors electron delocalization between the two semiconductors, suggests that all orientations of a particle relative to an external electric field will allow for excitons to be dissociated, stored, and released at a later time. While this approach, in principle, works, and fluorescence quenching of over 95% can be achieved electrically, we find that discrete trap states within the CdS are required to dissociate and store the exciton. These states are rapidly filled up with increasing excitation density, leading to a dramatic reduction in quenching efficiency. Charge separation is not instantaneous on the CdS excitonic antennae in which light absorption occurs, but arises from the relaxed exciton following hole localization in the core. Consequently, whereas strong electromodulation of the core exciton is observed, the core multiexciton and the CdS arm exciton are not affected by an external electric field
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A probabilistic prediction model for window opening during transition seasons in office building
Window operation of occupants in building has close relationship with indoor air quality, indoor thermal environment and building energy performance. The objective of this study was to understand occupants' interaction with window opening in transition seasons considering the influence of subject type (e.g. active and passive respondents) and to develop corresponding predictive models. An investigation was carried out in non-air-conditioned building in the UK covering the period from September to November. Outdoor temperature in this study was determined as good predictor for window operation. The differences in window opening probabilities between active and passive subjects were significant. Active occupants preferred to open window for fresh air or for indoor thermal condition adjustment, even though the outdoor air temperature sometimes were less than 12 °C. Proper utilization of windows in transition seasons contributed significantly to building energy saving and further improve energy efficiency in buildings
Influence of Fermion Velocity Renormalization on Dynamical Mass Generation in QED
We study dynamical fermion mass generation in (2+1)-dimensional quantum
electrodynamics with a gauge field coupling to massless Dirac fermions and
non-relativistic scalar bosons. We calculate the fermion velocity
renormalization and then examine its influence on dynamical mass generation by
using the Dyson-Schwinger equation. It is found that dynamical mass generation
takes place even after including the scalar bosons as long as the bosonic
compressibility parameter is sufficiently small. In addition, the fermion
velocity renormalization enhances the dynamically generated mass.Comment: 6 pages, 3 figures, Chinese Physics Letter, Vol 29, page 057401(2012
Electroweak Beautygenesis: From b {\to} s CP-violation to the Cosmic Baryon Asymmetry
We address the possibility that CP-violation in mixing may
help explain the origin of the cosmic baryon asymmetry. We propose a new
baryogenesis mechanism - "Electroweak Beautygenesis" - explicitly showing that
these two CP-violating phenomena can be sourced by a common CP-phase. As an
illustration, we work in the Two-Higgs-Doublet model. Because the relevant
CP-phase is flavor off-diagonal, this mechanism is less severely constrained by
null results of electric dipole moment searches than other scenarios. We show
how measurements of flavor observables by the D0, CDF, and LHCb collaborations
test this scenario.Comment: 4 pages, 1 figure, 1 tabl
Distributed Antittack Fault-Tolerant Tracking Control for Vehicle Platoon Systems Under Cyber-Physical Threats
Vehicle platoon systems are considered as automatous vehicles in a platoon-based driving pattern in which a following vehicle follows the preceding vehicle and maintains the desired vehicle spacing. This article investigates the leader-following tracking issue of vehicle platoon systems under cyber-physical threats with the distributed antiattack fault-tolerant tracking control strategy. In this study, vehicle platoon systems, complicated actuator faults in physical layer, and connectivity-mixed attacks in the cyber layer are modeled, respectively. Decentralized fault-estimation unknown input observer and distributed antiattack fault-tolerant tracking control designs are developed in an integrated control framework to guarantee the robust and resilient tracking property of estimation errors and platoon tracking errors as well as the reliable intervehicle spacing by virtue of attack activation rate and attack frequency metrics. Simulations validate the proposed distributed antiattack fault-tolerant tracking control algorithm in pernicious cyber-physical threatened scenarios
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